I know how tempting it can be, and I even thought about it. But, no, you can earn gems, just wait for a couple of months and you will have plenty. Each week we have a gem reward for downloading apps, 5g each, plus new goal each month can give you 12g if you master all 6 recipes. All makes 32g per month, and after 3 months you can have nearly 100g, isn't it great? And free?
It's the way I play the game. It's just game so let's make it as fun as you can. And by "fun" I mean not related to real money XD but it's just me you know, if you want to buy I think you should wait for gem sales when they offer you 40-50% off